The reasons the scintillation efficiency decrease of CsI(Tl) crystals exposed by the high-dosed radiation

The role of radiation defects in the light yield degradation of CsI(Tl) scintillation detectors has been investigated. The spectra and decay kinetic study of the luminescence of CsI(Tl) crystals coloured by γγ-radiation (Co60,106Gy) allowed to conclude that two types of the centres induced by irradiation absorb the luminescence of Tl+Tl+ centres responsible for the scintillations. The reabsorption of the Tl+Tl+ emission leads to the appearance of the long-wavelength luminescence caused by the colour centres of the first type. The luminescence of the centres of the second type is quenched at room temperature. These centres are not only deteriorating the efficiency of the activator luminescence, but also functioning as quenching centres to which the non-radiative energy transfer from Tl+Tl+ centres is realized.